Embodiments of the present invention relate to an organic opto-electric device and a method for manufacturing an organic opto-electric device. Further embodiments include the manufacturing of large area devices by means of an organic light-emitting diode structure (OLED) or by means of a solar cell as examples for organic opto-electric devices.
As a flat illuminated body with a moderate luminance as compared to a conventional light-emitting diode (LED), the OLED is ideally suitable for a manufacturing of flat diffuse light sources. Thus, on the basis of organic light-emitting diodes (OLED) new types of flat light elements may be implemented. These light sources are very promising and they are predicted a similar development as compared to the OLED based displays. By the used thin film technology it will become possible in the future to realize OLEDs also as flexible light bodies which enable completely new applications regarding the illumination of rooms.
As OLEDs represent current driven devices, a homogeneous current density distribution on large areas is an important point in the manufacturing of large area illuminated elements. Inhomogeneities in current density distribution along the large area luminous elements would be directly visible in fluctuations of luminosity and thus an accordingly homogeneous current supply is needed to achieve a uniform flat luminance.
As light generation is executed in an organic layer assembly or structure arranged between two electrodes, at least one transparent electrode is needed, so that the light may leave the OLED. The transparent contact is usually realized by a transparent conductive oxide (TCO) or by means of transparent metal layers, wherein the TCO layer or the transparent metal layer frequently comprise a low conductivity. Thus, the transparent contact limits the homogeneity of the current density distribution and thus the maximum size of the luminous surface. Large luminous surfaces would otherwise only be possible with great losses and the interconnected heat development, which is generally not acceptable.
A similar problem also exists with solar cells on the basis of organic materials which are very similar to the OLED regarding their setup. Due to the organic materials used, these structures however enable a conversion of optical radiation into electrical current, wherein this current is drained via the contacts. Also here the transparent electrical contact which is overcome by the incoming light reduces the maximum usable size of the device.
In order to still achieve larger areas (large OLEDs), for example, metal reinforcements in the form of nets (metal grids) are introduced into the exemplary TCO layer. These metal grids (also referred to as bus bars) reduce the effective layer resistance according to the occupancy and thus enable a realization of larger diode areas. Due to the non-transparency of these metal grids, however, the effective luminous surface is reduced. For this reason, metal grids are only sensible for up to approximately 25% of the TCO area. A sensible improvement would be the increase of the grid metal thickness, which is not sensible, however, due to the structuring possibilities and the layer thickness of the organic layer thickness. Another disadvantage apart from this is that the metal reinforced ITO layer is only contacted at the exterior edges which limits the maximum luminous element area or surface despite the effective reduction of the resistance.
As already mentioned above, OLEDs are current driven devices, so that for achieving a minimum luminosity a minimum current is needed which is to be supplied through each OLED portion as uniform as possible. To simultaneously limit the overall current, a parallel connection of OLED elements is unfavorable. What is better is a series connection as it was disclosed for example for conventional OLED structures in U.S. Pat. No. 7,307,278, U.S. Pat. No. 7,034,470 and U.S. Pat. No. 6,693,296. Apart from this, in DE 102007004509 A1 an improvement of the homogeneity by a second metalization level was achieved with a thick metal sheet which contacts the transparent contact layers with a low resistance. This second metalization plane thus enables a low resistance contact and thus the manufacturing of extensive light elements. The mentioned second metalization plane is here arranged on the non-transparent OLED electrode (first metalization plane). An electric insulation of the second metalization plane from the first metalization plane is achieved by an insulation layer. This insulation layer is interrupted in partial areas by open sites (so-called vias) through which the contact to the transparent (higher resistance) layer is achieved.
The disadvantages of conventional LED structures includes an inhomogeneous current density distribution or the reduction of the luminous efficacy caused by metal grids. Further disadvantages are visible transition areas in a series connection of OLED elements or the needed high current densities in a parallel connection.